Laboratory experiments were conducted to determine the impact of pozzolanic additives on the reaction of well cement paste under sequestration conditions. Two common blends consisting of class H cement and pozzolan/cement ratios of 35:65 and 65:35 were studied under CO2 exposure conditions of 2200 psi and 50 ∘C. Although the rate of chemical reaction is significantly greater than with neat cement paste, the alteration of physical properties is not sufficient to compromise sealing integrity under the conditions of the experiments.